Amino Acid Enriched Proteinous Wastes: Recovery and Reuse in Leather Making

Abstract

Environmental constraints have become the key issue for sustenance of industries worldwide. In leather industry, solid wastes create major problem to the environment, among which animal fleshing constitute a major portion. The main objective of this study is to evolve a simple, eco-benign method for the utilization of solid wastes to produce value added product. The product was developed by hydrolysis using alkaline protease (a novel Bacillus crolab 5468), which can be potentially used for surface upgradation of leather. Molecular mass of the polypeptides was found to be 9 kDa at 30 min and 6 kDa at 60 min of hydrolysis by MALDI-TOF. Furthermore, the polypeptides treated leather exhibited uniform grain pattern, better filling and strength properties compared to untreated leather. High value-added product presents a strong case for sustainable leather production as it adds both economic and environmental benefits to leather making.

Graphic Abstract

Appendices

Appendix A

The raw goat skins were taken and soaked in 300% water for 4–5 h. After soaking, the soaked skins were unhaired using 10% lime, 3% sodium sulphide, 20% water mixed and made as a paste and applied on the flesh side of the skins. The unhaired goat skins were subjected to reliming process containing 10% lime and 150% water for 48 h. These limed goat skins were defleshed using fleshing machine. After defleshing, the skins were delimed using 1% (w/w) ammonium chloride with 100% water (w/v) for 45 min in drum, followed by treatment with 1% (w/w) alkali bate for 30 min. The skins were washed and pickled with 8% (w/w) common salt and 80% (w/w) water for 10 min followed by acid treatment. 1% (v/w) sulphuric acid was given for 4 feeds at every 10 min interval and the drum was further run for 60 min. The final pH of pickled skin was 2.8 and the pickled skins were tanned using 8% (w/w) basic chromium sulphate (BCS) in half of the pickle bath for 90 min, then 50% (w/w) water was added and run for 30 min. Followed by which, a 1% (v/w) sodium formate was mixed with 10% (w/v) water and added to the running drum. After 30 min 1% (w/w) sodium bicarbonate was mixed with 10% (w/v) water and fed in 3 instalments at 10 min time intervals. Then, drum was continuously run for more than 60 min. In this process, the final pH of the float was observed to be 3.8.

Appendix B

The chrome tanned leathers (wet blue), produced from standard procedure was given in appendix I. The wet blue leather was washed with 100% (v/w) water in a drum for 10 min, the water was drained out and leathers were treated with neutralizing syntan 1% (v/w) in 100% (v/w) float in a drum and run for 20 min. After this, 0.5% (w/w) sodium formate and 0.5% (w/w) sodium bicarbonate were added to the running drum in 3 feeds at 10 min time interval. After the liquor attained a pH of 5.0, the leathers were washed twice with water 200% (v/w) for 10 min. After completion of washing, 100% (v/w) water with 3% (w/w) resin syntan were added to the drum and run for 20 min. Followed by this, dying was carried out using 2% (w/w) acid dye for 30 min and fat liquoring was carried out with synthetic fat liquor 4% (w/w) in the drum for 30 min. Subsequently melamine based re-tanning syntan 4% (w/w) was added and run for 40 min followed by the addition of synthetic fat liquor 4% (w/w), polymeric fat liquor 3% (w/w) and natural fat liquor oil 4% (w/w) and further running the drum for 40 min. Finally, the auxiliaries were leather was fixed using 2% (v/w) formic acid diluted with 20% (v/w) water and added at 3 feeds at every 10 min interval and the drum was further run for 30 min. After this, the leather was piled for overnight and were subjected to setting and hooked for drying. The dried leathers were staked and buffed using 400 grit emery papers.